NOVA bomb
From Halopedia, the Halo wiki
The Nova bomb is a UNSC prototype military weapon seen in the book Ghosts of Onyx. The Covenant grunt Huragok opened a message that gave a full description of the weapon.
Power
It has 100x power of the modern day weapon the H-Bomb and compresses to the density of a nutron star.
Materials
Nine fusion warheads
Message
From ''Ghosts of Onyx'': "This is the prototype Nova Bomb, nine fusion warheads encased in lithium triteride armor. When detonated, it compresses its fusionable material to neutron-star density, boosting the thermonuclear yield a hundredfold. I am Vise Admiral Danforth Whitcomb, temporarily in command of of the UNSC military base Reach. To the Covenant uglies that might be listening, you have a few seconds to pray to your dammed heathen gods. You all have a nice day in hell."
